MicroRNAs (miRNAs) are single-stranded noncoding RNAs and represent a novel class of recently discovered gene regulators. It is estimated that each miRNA controls hundreds of gene targets and that miRNAs are involved in the regulation of about 30% of all genes and almost every genetic pathway. Evidence suggests that they play important roles in developmental processes and viral infection, and they can function as oncogenes and tumor suppressors. Hence, it has been suggested that miRNAs and the components of the miRNA pathway can serve as targets for the discovery of novel therapeutic agents. Although the miRNA pathway is important in physiological and pathological processes, such as cancer development, to our knowledge, no small molecule inhibitor of this pathway has been identified. To fill this gap, a high-throughput cell-based assay will be developed for the screening of small molecule modulators of the miRNA pathway. This goal will be achieved through the following two specific aims: 1) a reporter system consisting of a luciferase gene fused to the binding site of human miRNA-21 (miR- 21) will be introduced into human HeLa cancer cells. Inhibition of the miRNA pathway by small molecules will lead to an increase of a luciferase reporter signal and thus provide an advantageous positive read-out. This assay will be used to screen small molecule libraries (>1000 compounds) in a high throughput fashion to discover molecules that interfere with the miRNA pathway. 2) Three secondary assays will be developed to validate and characterize the compound hits from the primary screen. These assays will exclude non-specific small molecule hits and deliver a more detailed picture of the miRNA pathway steps that are targeted by active compounds. Positive hits will be further investigated and improved through structure-activity relationship studies, via synthesis of second generation compound arrays. The information gained will ultimately lead to the elucidation of a specific target-small molecule interaction. Our long term goal is to develop chemical tools to better understand the molecular mechanisms of the miRNA biogenesis, the functions of specific miRNAs, and to assess the global impact of miRNAs on various cellular processes and pathways. Small molecules discovered in our screen are expected to have a broad impact on human health, due to the involvement of miRNAs in several human diseases (including cancer and viral infection) and the increasing interest in the miRNA pathway as a drug target. These molecules will be promising lead compounds for the development of new biological tools and new therapeutic agents. For example, chemical inhibitors against particular miRNAs, such as the clinically relevant miR-21, have the potential to be developed into novel anticancer therapeutics. Small molecules discovered in our screen are expected to have a broad impact on human health, due to the critical roles that miRNAs play in several human diseases such as cancer and viral infection. These molecules will be promising lead compounds for the development of new chemical tools in biomedical research and new therapeutic agents. Small molecule inhibitors against particular miRNAs, such as the clinically relevant miR-21, have the potential to be developed into novel cancer therapeutics. [unreadable] [unreadable] [unreadable]